---
title: 'Before Run Event | Cypress Node Events'
description: 'The before:run event fires before a run starts in Cypress.'
sidebar_label: 'before:run'
---

<ProductHeading product="app" />

# Before Run Event

The `before:run` event fires before a run starts. When running cypress via
`cypress open`, the event will fire when opening a project.

The event will fire each time `cypress run` executes. As a result, if running
your specs in [parallel](/cloud/features/smart-orchestration/parallelization), the
event will fire once for each machine on which the tests are run.

## Syntax

<WarningSetupNodeEvents />

:::caution

⚠️ When running via `cypress open`, the `before:run` event only fires if the
[experimentalInteractiveRunEvents flag](/app/references/experiments#Configuration)
is enabled.

:::

:::cypress-config-plugin-example

```ts
on('before:run', (details) => {
  /* ... */
})
```

:::

<Icon name="angle-right" /> **details _(Object)_**

Details of the run, including the project config, system information, and the
version of Cypress. More details are included when running via `cypress run`.

## Usage

You can return a promise from the `before:run` event handler and it will be
awaited before Cypress proceeds running your specs.

### Log the browser and the number of specs that will be run

:::cypress-config-plugin-example

```ts
on('before:run', (details) => {
  // details will look something like this when run via `cypress run`:
  // {
  //   config: {
  //     projectId: '12345',
  //     baseUrl: 'http://example.com/',
  //     viewportWidth: 1000,
  //     viewportHeight: 660,
  //     // ...more properties...
  //   },
  //   browser: {
  //     name: 'electron',
  //     version: '59.0.3071.115',
  //     // ...more properties...
  //   },
  //   system: {
  //     osName: 'darwin',
  //     osVersion: '16.7.0',
  //   }
  //   cypressVersion: '6.1.0',
  //   specs: [
  //     {
  //       name: 'login_cy.js',
  //       relative: 'cypress/e2e/login_cy.js',
  //       absolute: '/Users/janelane/app/cypress/e2e/login_cy.js',
  //     },
  //     // ... more specs
  //   ],
  //   specPattern: [
  //     '**/*.cy.{js,jsx,ts,tsx}'
  //   ],
  //   parallel: false,
  //   group: 'group-1',
  //   tag: 'tag-1'
  // }
  // details will look something like this when run via `cypress open`:
  // {
  //   config: {
  //     projectId: '12345',
  //     baseUrl: 'http://example.com/',
  //     viewportWidth: 1000,
  //     viewportHeight: 660,
  //     // ...more properties...
  //   },
  //   system: {
  //     osName: 'darwin',
  //     osVersion: '16.7.0',
  //   }
  //   cypressVersion: '7.0.0'
  // }
  if (details.specs && details.browser) {
    // details.specs and details.browser will be undefined in interactive mode
    console.log(
      'Running',
      details.specs.length,
      'specs in',
      details.browser.name
    )
  }
})
```

:::

## See also

- [After Run API](/api/node-events/after-run-api)
- [Before Spec API](/api/node-events/before-spec-api)
- [After Spec API](/api/node-events/after-spec-api)
- [How to use Plugins](/app/plugins/plugins-guide)
- [Node Events Overview](/api/node-events/overview)
